Wheat, and wheat produced in Japan in particular, is problematic in that it varies in quality depending on the production year. Reasons for this problem (particularly in Japan) include the production of many kinds of cultivar in a relatively small growing area and year-on-year weather conditions that affect seed quality. However, it is difficult to estimate the end use qualities of wheat seeds before full maturation. Hence, there is a risk of purchasing low-quality wheat. Therefore, development of technology for estimating the end use qualities of matured seeds (that will be obtained in the future) at an early stage has been desired.
Under such circumstances, certain genes correlative to the end use qualities of wheat have been reported. In particular, a high-molecular-weight glutenin subunit, puroindoline, and a waxy protein have been studied.
High-molecular-weight glutenin of wheat has long been studied as a protein that determines breadmaking qualities. Payne et al., have revealed the presence of genes encoding the high-molecular-weight glutenin on the long arm of chromosome 1 (Payne, P. I., Holt, L. M., Law, C. N. (1981) Theor Appl Genet 60: 229-236). These genes encode various types of subunits with different molecular weights. On chromosome 1D, a subunit pair (1Dx5+1Dy10) related to excellent breadmaking quality is present (Payne, P. I., Corfield, K. G., Holt, L. M., Blackman, J. A. (1981) J Sci Food Agric 32: 51-60). Comparison of the amino acid sequences between this subunit pair and a subunit pair (1Dx2+1Dy12) involved in poor breadmaking qualities has demonstrated that such types of the subunit pair are associated with gluten structure and physical characteristics (Flavell, R. B., Goldsbrough, A. P., Robert, L. S., Schnick, D., Thompson, R. D. (1989)). It has actually been reported that the gene transfer of 1Dx5 into wheat originally lacking 1Dx5 results in improvement of breadmaking qualities depending on the number of copies of the transferred gene (Barro, F., Rooke, B., Bekes, F., Gras, P., Tatham, A. S., Fido, R., Lazzeri, P. S., Shewry, P. R. and Barcelo, P. (1997) Nature Biotec 15: 1295-1299). Furthermore, the University of Florida has disclosed a method for transferring such high-molecular-weight glutenin subunit to improve breadmaking qualities (JP 2000-516097 A1).
Puroindoline has been identified as a “Grain Softness Protein,” which is a starch-binding protein in soft flour (Greenwell, P. and Schofield, J. (1986) Cereal Chem. 63: 379-380; and Jolly, C. J., Rahman, S., Kortt, A. A. and Higgins, T. J. V. (1993) Theor Appl Genet 86: 589-597). This protein was initially named friabirin and was revealed to have 2 major components homologous to lipid-binding proteins known as puroindoline “a” and puroindoline “b.” When the protein has been added to hard wheat flour containing no such protein, the amount of the protein added and bread hardness have exhibited inverse correlation. Accordingly, it has been demonstrated that puroindoline is a factor that affects bread quality (Dubreil, L., Meliande, S., Chiron, H., Compoint, J. P., Quillien, L. Branlard, G. and Marion, D. (1998) Cereal Chem. 75: 222-229).
Waxy proteins have also been studied as starch-binding proteins. There are 2 types of grain starch: linear amylose and amylopectin having a branched structure. A variety of grains, such as rice and barley, include “nonglutinous cultivars” containing both amylose and amylopectin molecules and “glutinous cultivars” containing no amylose. There have been no natural “glutinous” cultivars in wheat. However, the National Agricultural Research Center for the Tohoku Region has recently succeeded in developing glutinous wheat for the first time in the world. Whereas Wx proteins are present in nonglutinous wheat, Wx proteins are absent in glutinous wheat. Common wheat (Triticum aestivum L.) is a hexaploid having 3 types of Wx (Wx-A1, Wx-B1, and Wx-D1) on the chromosome arms 7AS, 4AL, and 7DS. JP Patent No. 3170595 discloses a method for confirming the presence or the absence of the expression of 3 types of Wx genes (Wx-A1, Wx-B1, and Wx-D1) in wheat through the use of a two-dimensional electrophoresis method. Furthermore, JP Patent No. 3170595 also discloses a method for producing glutinous wheat by using conventional crossing of wheat variants lacking the expression of two Wx genes. Moreover, JP 9-191819 A1 (1997) discloses bread that is produced using cereal flour including 0.5% to 30% by weight wheat flour produced from glutinous wheat. The produced bread shows no degradation in texture even when it is eaten after refrigeration or thawing following freezing. Genes encoding waxy proteins are known as waxy locus genes. JP 2003-284598 A1 discloses a method for detecting 3 types of variant waxy locus gene.
As described above, some genes governing the properties of protein and starch of wheat are known. The functions of such genes have been suggested by various kinds of test, including breadmaking tests, or examination of physical qualities of bread dough by using wheat flour milled from wheat produced by conventional breeding methods or genetic recombination.
However, the above findings merely demonstrate the relationship between specific genes and the end use qualities of wheat. Moreover, it is thought that many factors other than those above are related to the end use qualities of wheat. Therefore, it has been difficult to estimate the end use qualities of matured seeds during the growth stage before actual maturation.